feat: Add Armstrong Number

Signed-off-by: Supritha R S <suprithars111@gmail.com>

Author: suprithars111

Numbers/armstrong_number.cpp

@@ -0,0 +1,42 @@
+/*
+In recreational number theory, a narcissistic number is also known
+as a pluperfect digital invariant (PPDI), an Armstrong number or a
+plus perfect number is a number that is the sum of its digits
+each raised to the power of the number of digits.
+*/
+
+#include <bits/stdc++.h>
+using namespace std;
+
+// Function to check whether the Number is Armstrong Number or Not.
+
+bool is_armstrong(int n) {
+	if (n < 0) {
+		return false;
+	}
+	int sum = 0;
+	int var = n;
+	int number_of_digits = floor(log10(n) + 1);
+	while (var > 0) {
+		int rem = var % 10;
+		sum = sum + pow(rem, number_of_digits);
+		var = var / 10;
+	}
+	return n == sum;
+}
+
+int main() {
+	cout << "Enter the Number to check whether it is Armstrong Number or Not:" << endl;
+	int n;
+	cin >> n;
+	if (is_armstrong(n))
+		cout << n << " is Armstrong Number." << endl;
+	else
+		cout << n << " is Not Armstrong Number." << endl;
+	return 0;
+}
+
+/*
+Time Complexity: O(log(n))
+Space Complexity: O(1)
+*/